Before welding repair of steel castings, necessary pre welding preparations should be carried out. Firstly, it is necessary to determine whether to open a welding groove based on the defect nature of the steel casting to be welded. When necessary, the shape of the groove to be opened should be determined based on factors such as the defect size, location, depth, section thickness, and welding operation conditions of the parts. The groove preparation should be carried out according to the specified method. There are many methods for removing defects and preparing grooves, including common groove processing such as drilling, milling, and other mechanical processing, as well as pneumatic shovel cutting and polishing methods; Thermal cutting methods can also be used, such as oxygen cutting (neutral flame, flame core not less than 10mm from the surface of the steel casting), carbon arc gouging (only applicable to ZG230-450 and Grade B steel). If thermal cutting methods such as flame cutting and arc gouging are used to prepare the groove, the decarburized or carburized layer on the groove surface must also be removed after the groove is prepared to prevent the increase or decrease of carbon elements at the groove interface from affecting the mechanical properties of the weld repair area.
For crack defects in steel castings, it is necessary to first determine the initial end of the crack through certain methods. If necessary, it is necessary to drill a crack stop hole at the initial end of the crack, and then thoroughly remove the crack defects according to the above requirements to prevent the continuous expansion and extension of the crack.
The processing of the groove surface shall be based on exposing the metallic luster of the cast steel base material, and the transition between the bottom of the groove and the side wall must be conducted through an arc with a radius of not less than 5mm, without sharp corners. The 20mm range around the groove should also be removed to remove clean water, oil, rust, and other debris.
Before welding repair, the defective parts should be visually inspected again for confirmation. For the preparation of crack grooves with a defect length greater than 50mm, non-destructive testing methods such as MT magnetic particle or PT penetration should also be used for inspection. After confirming that the crack defects are completely removed, welding repair operations can be carried out.
When welding a through single sided groove, a backing can be added to the back of the groove or a back weld can be performed, but the backing used should be kept smooth and clean. If a steel backing is used, the chemical composition of the steel backing used should be the same or similar to that of the steel casting to be repaired by welding; When using non-metallic gaskets, ensure that the gaskets are not flammable. The backing after welding should be removed.
For thick sections with penetration defects, it is advisable to open double-sided grooves, leaving a gap of not less than 3mm at the root of the weld to ensure that the steel casting can be fully welded during welding repair. For the welding repair of double-sided grooves, before welding the reverse groove, the root of the front groove should be cleaned first to ensure that defects such as incomplete penetration, welding slag, and weld overlap at the root of the front groove are completely removed before welding the reverse groove.